The invention relates to a method for the production of synthetic gases, in particular reduction gases, from carbonaceous fuels, such as coal, coke, petroleum products, natural gas, coke oven gas, on the one hand, and oxygen-containing gases endothermally reacting with the fuels, such as steam and carbon dioxide, on the other hand, by reacting these starting products in a plasma reaction zone, as well as to an arrangement for carrying out the method.
Large amounts of synthesis or reduction gases of this type are required, for instance, in direct reduction plants for the production of iron sponge from iron oxides.
The supply to direct reduction plants operating with such gases hitherto has been realized by catalytically splitting natural gas in a so-called reformer in the presence of water and/or carbon dioxide. The resulting gas mixture, substantially comprised of carbon monoxide and hydrogen, is suited for the direct reduction of oxidic starting materials to metals. Such a reformer is composed of externally heated pipes filled with a catalyst--for instance, on a cobalt-nickel-base--through which the starting gas mixture is conducted and simultaneously reacted.
However, slight amounts of sulfur contained in the starting gas mixture may lead to a contamination, and thus inactivation, of the catalyst. Moreover, soot depositions on the catalyst mass occur again and again, which result in considerable production disturbances due to an undersupply, or interruptions in the supply, of reduction gas to the direct reduction plant. The pipe material of the reformers must resist very high temperatures of about 1,000.degree. C., and thus only high-temperature resistant alloys can be used as materials, for instance, chromium-nickel-based centrifugally cast parts. Even that material tends to intercrystalline corrosion, and thus to the formation of cracks, under the constant chemical and thermal loads. Therefore, both the catalyst and the pipes must be exchanged from time to time, which involves high costs.
The gasification of coal as well as the conversion of other gases or liquid carbon carriers into reduction gases has not been widely put into practice so far.
In German Offenlegungsschrift No. 3,104,281 a method is disclosed, in which a gas mixture substantially comprised of CO and H.sub.2 is formed in a gas generator from a fraction of a reaction gas of a shaft furnace, which gas has been freed from CO.sub.2 and H.sub.2 O, from a solid reductant as well as from an oxidant. The energy supply is effected by means of a plasma burner heating the reaction gas. As a solid reductant, in particular, carbon dust and as an oxidant, in particular, water are laterally blown into the heated gas. The ashes of the solid reductant collect on the bottom of the generator and are drawn off.
It is disadvantageous with this production of reduction gas that solid reductants or fuels are obligatory and the energy given off by the indirect plasma burner provided according to German Offenlegungsschrift No. 3,104,281 cannot be optimally utilized. This is so because the heat is given off from a plasma burner primarily by radiation and the contact zone with the reactants is very short.
In German patent No. 2,512,178 an arrangement for introducing hot reduction gases, produced by means of plasma energy, into the hearth of a blast furnace via tuyeres is described, which arrangement is comprised of at least one cylindrical plasma furnace arranged concentrically to the longitudinal axes of the tuyeres in front of the same. The plasma furnace is open both towards the tuyere and towards the hot-blast supply and, according to the embodiment illustrated, includes three radial indirect plasma burners offset to each other by 120.degree.. The arrangement described most specifically is designed to heat the hot blast of a shaft furnace to particularly high temperatures and is not suited for the production of synthetic gases in the sense of the above mentioned reformers.
In British patent No. 1,332,531 it is proposed to supply a hot reduction gas instead of blast to a shaft furnace, in particular a blast furnace, wherein the reduction gas is to be heated i.a. by plasma burners preferably arranged in the interior of the tuyeres of the shaft furnace. No details are given with respect to the production of the reduction gas from gaseous or liquid hydrocarbons and an oxygen-containing gas, but it is merely stated that these components may be supplied to the arc of a plasma simultaneously and in suitable portions. It has been found that the production of a reduction gas merely on the basis of these data is possible in practice only with an extremely unsatisfactory efficacy--if at all.